Method for producing a microlens array

Abstract

The invention relates to an optical microlens array producing method. The microlens array producing method according to the invention uses an intermediate material forming process for forming an intermediate material of photoresist on a flat sheet, the intermediate material having projections formed in the shape of a predetermined pattern; a resist master forming process of forming a resist master by heating the intermediate material to thereby smooth the surfaces of the projections; an inverted mold forming process for forming an inverted mold having a surface shape that is the inverse of the resist master; a clad portion forming process, for forming a clad portion having grooves equal in sectional shape to the inverted mold, using the inverted mold and also using a first light-transmitting material of a low refractive index; a process for forming microlenses by filling the concave portion of the clad portion with a second light-transmitting material which is higher in refractive index than the first light-transmitting material microlens with index than the first or the second light-transmitting.

What is claimed is: 
     
       1. A method for manufacturing a microlens array, comprising the steps of: forming an intermediate material of photoresist on a flat sheet, the intermediate material comprising at least one projection formed in the shape of a predetermined pattern;   forming a resist master by heating the intermediate material to a temperature whereby the surfaces of the at least one projection are smoothed under the influence of surface tension;   forming a stamper having an inverted surface shape of said resist master; and   forming a microlens array using said stamper and a light-transmitting material.   
     
     
       2. The method according to claim 1, wherein said light-transmitting material is an ultraviolet light curing resin. 
     
     
       3. The method according to claim 2, wherein said process for forming the intermediate material comprises the steps of: forming a photoresist layer on said flat sheet;   exposing the photoresist layer to ultraviolet light from above a photomask placed on the photoresist layer, said photomask having a light shielding portion in conformity with a microlens pattern;   dissolving the photoresist which has been radiated by the ultraviolet light by a developer; and   washing away the photoresist which has been dissolved to form at least one projection of the photoresist layer in conformity with the microlens pattern on said flat sheet.   
     
     
       4. The method according to claim 3, wherein said process for forming the resist master comprises the steps of: heat-melting the projection of the photoresist layer in conformity with the microlens pattern on said flat sheet and smoothing the surface of the projection.   
     
     
       5. The method according to claim 4, wherein said process for forming the stamper comprises the steps of: forming an electroconductive nickel film on the surface of said resist master having the projection;   forming a nickel layer on said resist master incorporating the nickel film;   separating said flat sheet from said resist master with said first nickel layer formed thereon;   removing the projection remaining in a recess in said nickel layer.   
     
     
       6. The method according to claim 5, wherein said process for forming the microlens array comprises the steps of: positioning a transparent sheet in parallel with but offset from the projection side of said stamper by a fine gap;   pouring the ultraviolet light curing resin into the gap;   radiating a ultraviolet light onto the ultraviolet light curing resin from above said transparent sheet; and   separating said stamper from both said transparent sheet and the ultraviolet light curing resin.   
     
     
       7. The method according to claim 1, wherein said process for forming said microlens array is performed in an oxygen-free atmosphere. 
     
     
       8. The method according to claim 1, wherein a plurality of projections are formed and each projection is completely separated from the other of the projections. 
     
     
       9. The method according to claim 1, wherein the section of the intermediate material changes from substantially rectangular shape to substantially semicircular shape by heating the intermediate material.